Starting control for split-phase motors



Od. l, 1957 H, F, CLARK 2,808,553

STARTING CONTROL FOR SPLIT-PHASE MOTORS Filed May 25, 1954 2 4. 6 a Io 'l2 I4 |6 I8 Attorney United States Patent Otitice Patented Oct. 1, 1957 STARTING CONTROL FOR SPLIT-PHASE MOTORS Harry F. Clark, Dayton, Ohio, assigner to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application May 25, 1954, Serial No. 432,140

3 Claims. (Cl. S18-221) This invention relates to electrical apparatus and more particularly to split phase motor starting controls.

It is an object of my invention to provide a simple low cost current type of electromagnetic starting relay which is snap-acting and which is closed during each idle period and at each motor start and which is opened when the motor reaches a speed between peak torque and balance speed.

This and other objects are attained in the form shown in which `an armature is connected to a normally closed toggle snap-action switch mechanism connected in series with the phase winding. The electromagnet cooperating with the armature is provided with two opposed coils one in series with the main winding and one in series with the phase winding. When these coils are about equal the magnetic force of the electromagnet will be insuicient to overcome the force of the snap-action mechanism at the motor start. However, the resultant force increases as the motor speed increases and at a point between peak torque and balance speed will be suiicient to overcome the snap-action mechanism to attract and pull in the armature and move the phase winding contacts to the open circuit position with snap action. The return spring of the armature is provided with sutilcient spring force to overcome snap-action mechanism to return the armature and the phase winding contacts to the closed circuit position when the motor is deenergized.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the linvention is clearly shown.

In the drawings:

Figure l is a top view of a control embodying one form of my invention together with a motor and wiring diagram;

Figure 2 is a vector diagram showing the diierence in magnetic force at the motor start; and

Figure 3 is a similar vector diagram showing the difference in the electromagnetic force at balance speed.

Referring now to the drawing there are shown the supply conductors 20 and 22. The supply conductor 22 is connected to the common terminal of the main winding 24 and the phase winding 26 of an electric motor 28. The supply conductor 2t) is connected through a control switch .36 and the conductor 32 to an L-shaped contact and terminal 34 which is fastened to a thin rectangular base 35 of electrical insulating material. The contact 34 is normally engaged by a movable contact 36 mounted upon the movable portion of a reverse L-shaped cantilever bimetal 3S having its base portion welded to a reverse L-shaped metal frame member 40.

This reverse L-shaped frame member 40 is in the form of a metal strip mounted edgewise upon the base 35. Connected to another portion of the frame member 40 is a hook-shaped bimetal member 42 provided with an integral stifening rib. The free end of the hook-shaped compen sating bimetal 42 is connected by a C-shaped toggle spring 44 to the free end portion of the bimetal 38. The members 34 to 44 inclusive constitute a self-heated bimetal type overload protector in which the bimetal 38 is connected in series with the supply conductor 20 and the bimetal 42 serves to compensate for variations in ambient temperature.

The frame member is connected by a conductor 46 to the common junction of two electromagnet coils 48 and 59 of insulated magnet wire which are wrapped around the core 52 between the upper bent over end 54 and a lower offset portion 56. The upper end of the coil 48 is connected by the conductor 58 to the main winding terminal 60 which in turn is connected beneath the base 35 by the conductor 62 to the second end of the main winding 24. The opposite end of the coil 50 is connected electrically to the core 52 adjacent the cifset 56.

The lower end of the oiset portion 56 is provided with a thin leaf spring hinge 64 to which is connected the armature bar 66. This armature bar 66 has a portion provided with wrapped insulation 68 to prevent it from beingelectrically connected to the stationary phase winding contact 7i). The upper end of the armature bar 66 is provided with a bracket 72 to which is pivotally connected a Ceshaped toggle spring 74. The C-shaped toggle spring 74 is pivotally connected to a leaf spring 76 carrying a contact 7S adapted to engage the stationary phase winding contact 70. The lower end of the leaf spring 76 is provided with an oiset Sil which is welded to the lower end of the hinge spring 64 and the lower offset portion 56 of the core 52. The base 3S is provided with an edge mounted stop bar 82 located between the bimetal 38 and the spring Contact carrying member 76 which serves to limit the opening movements of the bimetal 38 and the contact strip 76.

The control is shown in the position it assumes when the motor is deenergized. The motor 23 is energized by closing the switch 36. This allows current to ilow from the supply conductor 20 through the conductor 32, the terminal and Contact 34, the contact 36, the bimetal 38 and the conductor 46 to the junction of the coils 48 and 50. The phase winding current lows downwardly through the coil 5t) to its connection with the core 52 and thence through the core 52 to the contact strip 76 and the contacts 78 and 70 to and through the phase winding conductor 84 to the second terminal of the phase winding 26. The main winding current ows upwardly through the coil 48, the conductor 58, the terminal and the conductor 62 to the other terminal of the main winding 24.

The currents and forces in the main winding coil 48 and the phase winding coil 50 are shown in vector diagrams in Figures 2 and 3. Since these create substantially opposed magnetic forces, the resultant force indicated by the dotted arrow 86 is comparatively small `and its attraction upon the armature bar 66 is insufficient to overcome the force of the C-shaped toggle spring 74. As the motor speed increases, the main winding current diminishes much more rapidly than the phase winding current. The difference between the current in the two windings also grows so that at balance speed the amount of effective electromagnetic force upon the armature 66 is represented by the dot and `dash arrow 8S. Before this value is reached, the armature 66 is attracted suliciently to overcome the force of the toggle spring 74 to move the armature toward the core 52 and to cause the toggle spring 74 and the contact carrying leaf spring 76 to snap away from the contact into contact with the stop 82.

This will open the phase winding circuit and continue the operation on the main winding 24 alone. The opening of the phase winding circuits substantially deenergizes the coil 50 but the armature 66 continues to be held attracted by the smaller current flowing through the coil 48. This current is sutlicient to prevent the armalture 66 from being released.

It should be understood that when the armature 66 is in the attracted position there is a certain amount of force from the toggle spring 74 which aids in keeping the armature attracted. The upper end of the armature 66 may be provided with one o1' two weights 90 to prevent any chattering or vibration due to the use of alternating current. The armature 66 may also be provided with a felt pad 92 to cushion the movement of the armature 66 into engagement with the coil 48 and the core 52.

When the motor circuitis deenergized by opening the switch .30 or by opening the contacts 34 and 36, the electromagnetic attraction of the core 52 for the armature 66 ceases. The leaf spring 64 has suicient force to overcome the toggle spring 74 and to move the armature 66 back to the position shown in Figure 1. This prepares the control for a new start.

in accordance with the provisions `of Rule 78a, ref crence is made to the following prior led application: S. N. 361,198, led June 12, 1953.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted as may come within the scope of the claims which follow.

What is claimed is as follows:

1. A starting control for a split phase electric motor having main and phase windings including an armature, a normally clesed snap-action contact mechanism connected to said armature for controlling the energization of the phase winding, an electromagnet having two windings constituting the only electromagnetic force for attracting and releasing said armature, one of said windings being connected to said phase winding and the other winding being connected to the main winding, said two windings being arranged in opposed relationship and proportioned so that the total attraction for the armature is at a minimum under motor starting conditions, said snap-action contact mechanism having suicient resistance to the attraction of said electromagnet at low motor speeds to prevent its opening until the motor approaches its balancing speed.

2. A starting control for a split phase electric motor having main and phase windings including an armature, a toggle spring pivotally connected to said armature, a normally closed contact device pivotally connected to said toggle spring, an electromagnet having two windings constituting the only electromagnetic force for attracting and releasing said armature, one of said windings being connected in series with the phase winding and the other winding being connected in series with the main winding, said toggle spring having sufficient force opposing the attraction of said electromagnet at -low motor speeds to prevent the opening of said contact device until the motor approaches its balancing speed and during the remainder ot the period of operation opposes the reopening of the normally closed contact device.

3. A starting control for a split phase electric motor having main and phase windings including an armature, a toggle spring pivotally connected to said armature, a normally closed contact device pivotally connected to said toggle spring, an electromagnet having two windings for attracting and releasing said armature, one of said windings being connected in series with the phase winding and the other winding being connected in series with the main winding, said two windingsv being arranged in opposed relationship and proportioned so that the total attraction for the armature is at a minimum under motor starting conditions, said toggle spring having sufficient force opposing the attraction of said electromagnet at low motor speeds to prevent the opening of said contact device until the motor approaches its balancing speed, and a return spring for said contact device having sulicicnt force to overcome and operate said toggle spring and said contact device to closed position when said electromagnet is deenergized.

References Cited in the le of this patent UNlTED STATES PATENTS 1,542,709 Larson June 16, 1925 1,981,259 Wertz Nov. 20, 1934 2,021,199 Pearce Nov. 19, 1935 2,170,748 Eaton Aug. 22, 1939 2,235,537 Shaefer Mar. 18, 1941 2,237,705 Kohl Apr. 8, 1941 2,447,488 Clark Aug. 24, 1948 2,456,112 Dodd Dec. 14, 1948 2,475,038 Lucas July 5, 1949 2,477,120 Ecker July 26, 1949 2,491,643 Burks Dec. 20, 1949 2,548,148 Fisher et al. Apr. 10, 1951 2,576,681 Hall Nov. 27, 1951 FOREIGN PATENTS 845,757 France May 22, 1939 

